The present invention relates to a gas laser tube and, more particularly, to an improvement in the electrode structure thereof.
A gas laser tube, such as a He-Ne gas laser tube of the structure shown in FIG. 1, is conventionally known.
Referring to FIG. 1, a capillary tube 11 of an insulating material such as glass is coaxially disposed within a cylindrical envelope 13 of glass. End tubes 16a and 16b of diameter smaller than that of the envelope 13 are connected to both ends of the envelope. One end tube 16b at the end wall of the envelope 13 is connected to the capillary tube 11. A pair of reflective mirrors 12a and 12b are disposed at the end parts of the two end tubes 16a and 16b, respectively.
The capillary tube 11 forms a single discharge path between the anode and the cathode and a laser medium, for example, a He-Ne gas mixture is sealed therein. The electrical energy is converted into light energy by the discharge of this He-Ne gas mixture. The capillary tube 11, in addition to this, functions to amplify the converted light and to determine the transversal mode of the laser beam by its position relative to a resonator structure.
The paired reflective mirrors 12a and 12b arranged at the end parts of the pair of end tubes 16a and 16b, respectively, are reflective mirrors of small light loss, prepared by depositing a dielectric multi-layer film on a glass substrate. One reflective mirror 12a has a reflectance of substantially 100% and the other reflective mirror 12b has a reflectance of 95 to 99%. The laser beam is provided from the reflective mirror 12b. These paired reflective mirrors 12a and 12b are disposed perpendicularly to the axis of the capillary tube 11 in such a manner that they are parallel to each other with high precision (e.g., with 1 m resonator length and within an inclination of 0.1 milliradian) and comprise a resonator.
A cylindrical cathode 14 of aluminum or the like, the surface of which is oxidized, is disposed inside the cylindrical envelope 13. This cathode 14 is electrically connected through a conductor 18 to a cathode terminal 15 protruding from an end wall 19 of the envelope 13. An anode terminal 17 is implanted in the end tube 16b substantially perpendicularly to its axis. Accordingly, the cathode terminal 15 and the anode terminal 17 are at right angles.
In a laser tube of this structure, the anode terminal 17 has the following defects as to its position and shape. Since the cathode terminal 15 and the anode terminal 17 are not parallel to each other as in the case of a cathode ray tube or the like, a special socket for these terminals is difficult to prepare. Further, the anode terminal 17 is mounted to the end tube 16b of small diameter. Accordingly, when the external lead wire is connected to the anode terminal 17, and an external force is exerted on this lead wire, the anode terminal 17 is pulled. When this force is exerted on the implanted part of the terminal 17, the end tube 16b becomes bent. Consequently, the surface of the reflective mirror 12b mounted with high precision at the end part of the end tube 16 becomes inclined, resulting in instability or a drop in the output of the laser beam. When a further force is exerted in connecting the lead wire to the anode terminal, the end tube 16b may be broken. The heat generated by discharge of the laser tube causes a temperature gradient in the direction perpendicular to the tube axis, that is, in the vertical direction. The thermal expansion caused by this acts to bend the laser tube. This phenomenon is unavoidable for a laser tube regardless of its scale. When this phenomenon is extreme, the laser oscillation may be interrupted due to this phenomenon. Since the end tubes 16a and 16b are small in diameter, they are more susceptible to the effects of this phenomenon. The mounting of the anode terminal 17 to the end tube 16b results in asymmetry of the end tubes 16a and 16b, adversely affecting the output stability and the beam stability. Although a ring-shaped anode terminal comprising a part of the end tube is known, it has drawbacks in that much labor and many parts are required for hermetic sealing.